Merged DDWFTTW in a “Real” Wind

[69dodge]

I don't understand this "propeller wind" and "driving wind". There's just air.

What wrong with saying that the point you're talking about is right where the propeller hits the air?

 

[humber]

Humber claims such a cart that is not wind powered, and that such a thing is possible without extracting energy from the wind, or anything else. His claim is that an unpowered cart can go downwind at wind speed, only he doesn't realize it because he doesn't understand reference frame equivalence.

Your mistake is to think that the TM has anything to do with a cart in the wind.
The ddw cart is a fraud. Simple at that.

 

[humber]

It's so rarely worth responding to an RCP post, but yes, I remember that well. The guy is an idiot.



Even a broken clock is right twice a day. Look at ynot. He finally convinced himself that DDWFTTW works despite his best efforts, but he doesn't have a clue why.

Your cart is a fraud, Spork.
The balloon in a car shows how little you understand.

 

[humber]

Not to mention the fact that we put a tell-tale well above the highest point of the prop and made it point straight aft while going DDW.

To be fair JB, Ynot doesn't understand the basics of how this works. It's not reasonable to expect him to understand this.

Apologizing for success?
Like the balloon in the car, such use of streamers shows that you are willing to video basic errors.

 

[spork]

There is a region behind the propeller where the opposing winds interact with each other and create an area of pressure.

This is not true. I suggest you label your theories as such rather than to make false claims and pass them off as fact.

 

[spork]

I don't understand this "propeller wind" and "driving wind". There's just air.

Bingo. Of course we've told ynot that many times. But knowing everything is the greatest impediment to learning anything.

 

[ynot]

[FONT=Verdana, sans-serif]

I don't understand this "propeller wind" and "driving wind". There's just air.

[/FONT]
[FONT=Verdana, sans-serif]Sure air is air but it has different properties in different places as winds. I call the “natural” wind a “driving wind” and the wind being produced by the propeller a “propeller wind” to clearly identify which wind I'm talking about.[/FONT]

[FONT=Verdana, sans-serif]

What wrong with saying that the point you're talking about is right where the propeller hits the air?

[/FONT]
[FONT=Verdana, sans-serif]Because the propeller is moving faster downwind than the driving wind and therefore hits the air as a headwind not a driving wind. Where the propeller hits the air therefore can't possibly be the transfer point.[/FONT]

 

[69dodge]

Because the propeller is moving faster downwind than the driving wind and therefore hits the air as a headwind not a driving wind. Where the propeller hits the air therefore can't possibly be the transfer point.

Yes, in a sense the propeller as a whole feels a headwind. But the propeller is spinning quickly. So its twisted blades can still be pushed forward by the air, even though the air is moving backward relative to the cart.

This is why I asked you about how a fan works.

If you focus on a bit of air in the path of a spinning propeller blade, the air gets pushed backward by the blade, not because any one point on the blade is moving backward---it isn't, it's moving around in a circle---but because the bit of air successively encounters different points on the blade as it spins. Later points are further back than earlier points because the blade is twisted, so the effect on the air is roughly the same as if it were pushed by a backward-moving surface. Or, to say the same thing the other way around, the effect on the propeller is roughly the same as if it were pushed by forward-moving air.

 

[humber]

[FONT=Verdana, sans-serif]Because the propeller is moving faster downwind than the driving wind and therefore hits the air as a headwind not a driving wind. Where the propeller hits the air therefore can't possibly be the transfer point.[/FONT]

That's one way of expressing it. If the cart is faster than the wind, there will be a headwind.

An above WS cart accelerates that slower air before it, so the force in reaction to that, opposes the cart.
The blades of the rotor will experience the same force, and it makes no difference if it is turning or not.

The cart is a sham.
The BB is explained by changing wind patterns, and the data confirms that.
There is no ddw record.

 

[humber]

Yes, in a sense the propeller as a whole feels a headwind. But the propeller is spinning quickly. So its twisted blades can still be pushed forward by the air, even though the air is moving backward relative to the cart.

This is why I asked you about how a fan works.

If you focus on a bit of air in the path of a spinning propeller blade, the air gets pushed backward by the blade, not because any one point on the blade is moving backward---it isn't, it's moving around in a circle---but because the bit of air successively encounters different points on the blade as it spins. Later points are further back than earlier points because the blade is twisted, so the effect on the air is roughly the same as if it were pushed by a backward-moving surface. Or, to say the same thing the other way around, the effect on the propeller is roughly the same as if it were pushed by forward-moving air.

Well, that contains a lot of hand-waving terms, of pushing, and this moving faster than that, whereas the physics of props and turbines is all about acceleration of the air.

Well advanced science, that along with the laws of thermodynamics and the commonsense idea that a car can't be driven by its own headwind, say it is more likely that two rank amateurs from California are wrong, than all of physics is wrong.

 

[A.T.]

The cart is ONLY powered by the wind.

Nope, what it's 'powered' by is frame dependent -- it can also be powered ONLY by the ground if analyized in a frame moving the speed of the wind.

It depends what ynot means by "wind". If he means "true wind" then his statement is correct in any frame. You assume that by "wind" he means the airmass.

 

[A.T.]

“It blows air backwards in to an opposing wind..

Try to be more precise and use physical terms. "Blows air backwards" probably means "accelerates air backwards".

But what do you mean by "opposing wind"? Which weird reference frame are you considering, where the air in the prop wake is moving in the opposite direction of the air in the free stream? It is definitely neither the ground frame, nor the free stream airmass frame, nor the cart frame.

Your statement is true in some frames that move slightly below windspeed, but I don't see how this frame dependent issue somehow explains the mechanism in general. And you don't explain that either:

... and it gets pushed forward by a combination of both winds”.

What do you mean by "pushed by a combination winds" in physical terms? Things get pushed by forces. "Winds" are not forces, they are velocities of air relative to something.

 

[windgrins]

The cart is powered only by the wind.

Why is this wrong?

The cart is ONLY powered by the wind.

Ynot,

I believe if this discussion hadn't reached this pedantic level, the statement would have been reasonably acceptable on face value. It does encapsulate the idea that there is no other energy source other than the air moving over the ground.

The point is, that it gives no insight to the concept of the unseen and forgotten component (the ground) as every bit as important as the propeller in the air. Just like a sailboat on an upwind tack, the keel (or water interface) is equally important as the sail (or air interface.) The point is that for the normal functioning of a sailboat, the utilizable energy and functioning of the boat derive equally from the sail and keel. (underlined to stress.)

This keel concept (which is so often ignored) is translated into the BB and the other DDWFTTW carts by the wheel/drivetrain arrangement. It is essential for the functioning of the cart.

My comment is, not that it is wrong, but incomplete, towards a clear concise thorough understanding of the carts mode of operation. This is of course why so many go on about the differential between the speed of the airmass and ground in the explanations of the functioning of the cart. Those that don't get this concept have no hope of understanding how it works.

Does this help?

Regards,

Windgrins

 

[windgrins]

Point of transfer of energy

Yes but the wind created by the propeller is still going slower than the driving wind. If the Cart went faster than the driving wind at the same speed as the propeller wind then the propeller wind would be still relative to the driving wind and the cart would have reached maximum speed.

Opposing winds aren't like opposing light beams that don't interact with each other. There is a region behind the propeller where the opposing winds interact with each other and create an area of pressure. I believe this area is quite close to the propeller blades. For the energy of the wind to transfer to the cart there has to be a point of transfer. I believe this point of transfer is this area of pressure. If anyone thinks the point of transfer is in a different place please explain exactly where it is.

Ynot,

The two points of transfer of energy for the vehicle is the tangent point of the wheel to the ground and the air molecules impacting the prop blade.

There is not a mysterious "cushion of air of prop blast and wind". It is a continuous medium and the flow through the prop is simply accelerated from front to back at all times once the prop is unstalled. This is much like an airplane starting from a standstill on a runway. There never is a "cushion" of air.

Regards,

WindGrins

 

[windgrins]

Simulation question

Open Question to the group:

Does anyone on the forum have the skillset to create a simple simulation in something like X-plane or any other aero simulator so that the group can visulize the flow lines around the prop in the four regimes?:

standing start
slower than the wind
WS
substantially faster than the wind.

This wouldn't prove anything, but would be enormously helpful in the visualization of the machines functioning.

Regards,

WindGrins

 

[ThinAirDesigns]

I clearly defined the frame my description and questions were based on . . .

LOL -- What a TOTAL crock of ...

*Nowhere* do you even *mention* a frame of reference in your description and question list, let alone "clearly define" one.

Your entire post:
http://www.internationalskeptics.com/forums/showthread.php?p=7115713#post7115713

JB

 

[windgrins]

Question for Spork?

Consider the work done. Work is force x distance. In a given amount of time the cart moves a much smaller distance through the air than it does over the ground. Thus, the same amount of force acting on that parcel of air represents less work.

Consider trying to push a car at 1 mph vs. trying to push that same car at 10 mph. The latter will take 10 times the energy.

Spork,

It's a nit. Is this a drag statement, a rolling friction statement, KE statement, or something else? I don't see how the statement in blue can be true any way I've sliced it.

Would you please explain?

WindGrins

 

[ThinAirDesigns]

You assume that by "wind" he means the airmass.

Yes, I have assumed that because in endless related references, he keeps referring to the "airmass" when speaking about the wind.

As you and others point out, there are several simple additive ways to make his first statement (of the three) perfectly correct. He has no such out for the other two statements in that group.

JB

 

[zooterkin]

The cart is a sham.
The BB is explained by changing wind patterns, and the data confirms that.
There is no ddw record.

You'll be publishing your analysis of the data which proves this shortly, I trust?

 

[ThinAirDesigns]

Ynot,

I believe if this discussion hadn't reached this pedantic level, the statement would have been reasonably acceptable on face value. It does encapsulate the idea that there is no other energy source other than the air moving over the ground.

You're at least more than half right here windgrins. In casual reference we regularly call the cart "wind powered". In fact, our stated mission was "Directly downwind, faster than the wind, powered only by the wind, steady state".

However, even Ynot understands (well, maybe) how his statement is flawed in a technical sense since he now is attempting to falsely claim that he defined the frame.

Your point is totally correct that the level of detail required for an exhange depends on the level of the exchange.

JB